非水介质中酶催化的反应研究新进展

介绍了非水介质中酶催化反应有机合成中的应用及手性化合物的酶促拆分与合 成反应，分析了冷冻干燥保护剂和修饰剂对酶性质的影响，论述了固定化酶在有机 溶剂中的应用，并讨论了影响固定化酶性质的因素。     

非水溶剂中酶反应研究进展

本文报道了在非水溶剂系统中进行酶促反应的最新进展。对于酶反应的低水体系与必需水，酶活性与非水介质性质之间的关系，疏水参数ｌｏｇＰ，介质工程与酶经酶经配体印迹后，其活性比未经印迹的酶活性明显提高等进行了介绍，并举例说明了在非水溶剂中进行酶促反应的应用前景。     

离子液体的制备及其在酶催化反应中的应用

离子液体，尤其是非水溶性离子液体可以作为一种溶剂或酶的载体用于非水相酶促反应中，也可以用于双相体系中的酶促反应。本文概括性介绍了常见离子液体的制备，总结和讨论了离子液体中酶的活性、稳定性、反应选择性以及各类酶在离子液体中的催化反应行为。离子液体的物性及其与酶的相容性对酶本身及酶促反应都有很大的影响。在非水相酶促反应中，离子液体的极性作用不遵从通常用来判别大多数有机物溶剂行为的规则，比如lgP规则。     

离子液体中酶促区域选择性合成CFAE

碳水化合物脂肪酸酯(CFAE)作为一类非离子型生物表面活性剂,被广泛用于食品、医药及化妆品工业,一些CFAE还具有抗菌、抗肿瘤等特殊生物活性。非水介质中酶促区域选择性合成CFAE反应的瓶颈在于高极性碳水化合物与酰基供体不易相溶,并具有多个可酰化羟基。传统有机溶剂虽能提高极性底物在体系中溶解度,但常使酶活下降。新型绿色介质离子液体用于CFAE的酶法合成过程具有诸多优点,不仅生物催化剂能维持较好的活性与稳定性,且良好的底物溶解性可改善反应区域选择性及转化速率,反应体系还可重复利用。本文介绍了离子液体中影响酶促区域选择性合成CFAE反应的主要因素,包括酶、底物在离子液体中的溶解性能及底物自身性质等,详述了离子液体中酶促制备CFAE的研究进展,也指出了酶促合成CFAE存在的问题与发展前景。     

无溶剂体系中的脂肪酶催化反应研究进展

酶作为一种生物催化剂，具有专一性强、催化效率高、在常温常压等温和条件下能进行操作等优点，从而引起众多学者的兴趣．传统酶学研究的是酶在水溶液中的催化行为，这使得人们产生了误解，认为只有在水溶液中酶才能保持活性，有机溶剂会使酶变性失活．1984年，美国麻省理工工学院的科学家Klibanov首次发现有许多酶可用于有机溶剂，从而解决了有机化合物在水介质中的低溶解性限制酶催化剂应用的问题，酶不仅能够在有机溶剂中保持稳定，而且还显示出很高的催化转酯活力．这一发现为酶学研究和应用带来了又一次革命性飞跃，从而促进了非水酶学的兴起，使之成为目前重要的酶技术之一．其中研究较多的是脂肪酶，脂肪酶不仅能催化油脂水解，而且在非水介质中也能催化油脂的酯交换反应，用来提高油脂的品位．随着研究的深入和学科的交叉，各种新的酶促反应体系也相继被发现，大大拓宽了酶催化反应的应用范围，使酶法合成逐步发展成为与化学法合成相互补充的合成方法．近年来非水介质中的不同反应体系的酶催化反应，主要有：有机溶剂体系、反相胶束体系、超临界体系、气相体系等，其中无溶剂体系中的酶促反应是非水体系中酶促反应的特例．     

超临界二氧化碳流体在酶催化反应中的应用

酶催化反应已发展到了利用超临界二氧化碳流体为介质来进行。文章评述了在超临界二氧化碳中影响酶活性和稳定性的重要因素，介绍了SCCO2介质中酶催化反应的最新进展。     

过氧化物酶催化酚聚合的研究

研究过氧化物酶在非水介质中催化酚类化合物的聚合。探讨了有机溶剂的浓度，溶剂极性，体系ＰＨ值、酶浓度等因素对聚酚分子量的影响；分析了聚酚的链结构。结果表明，酚分子之间通过酚羟基的邻位或对位相互连结。形成了分子链上带有酚羟基的聚酚树脂；通过调节聚合参数，可以改变聚酚的分子量。     

非水介质中的酶催化反应

介绍了非水溶剂体系中的酶催化反应，主要是反胶束体系中酶催化反应和脂肪酶催化反应的新研究成果，评述了各溶剂体系中酶的结构，动力学特征，稳定性及活性。     

醇腈酶促不对称合成手性氰醇反应条件的研究

利用气相色谱手性分析,对醇腈酶促不对称合成手性氰醇中的pH值、温度、底物浓度和水含量对酶反应速度和非酶反应速度的影响作了研究。结果表明,上述因素对酶反应和非酶反应速度均有显著影响。在水含量较低的非水相酶反应体系中,pH值在4．0以下或反应温度为0－5℃时,非酶反应受到较大程度的抑制,而酶反应仍具有相对较快的反应速度,故可获得高光学纯度的产物。     

非水介质中曲克芦丁乙烯酯的酶促合成

在非水介质中,选择性催化曲克芦丁羟乙基上的伯羟基发生酯交换反应,合成一系列曲克芦丁乙烯酯.同时考察了酶源、酶量、反应介质、酰化试剂链长、溶剂含水量、反应时间等因素对曲克芦丁酶促酯交换反应区域选择性的影响.结果表明:以吡啶为溶剂,其含水量1%时,枯草杆菌碱性蛋白酶催化活性最高,随着酰基供体碳链的减少,产率增大,且反应达平衡的时间缩短.     

Modified enzymes for reactions in organic solvents

Recent studies on biocatalysis in water—organic solvent biphasic systems have shown that many enzymes retain their catalytic activities in the presence of high concentrations of organic solvents. However, not all enzymes are organic solvent tolerant, and most have limited and selective tolerance to particular organic solvents. Protein modification or protein tailoring is an approach to alter the characteristics of enzymes, including solubility in organic solvents. Particular amino acids may play pivotal roles in the catalytic ability of the protein. Attaching soluble modifiers to the protein molecule may alter its conformation and the overall polarity of the molecule. Enzymes, in particular lipases, have been chemically modified by attachment of aldehydes, polyethylene glycols, and imidoesters. These modifications alter the hydrophobicity and conformation of the enzymes, resulting in changes in the microenvironment of the enzymes. By these modifications, newly acquired properties such as enhancement of activity and stability and changes in specificity and solubility in organic solvents are obtained. Modified lipases were found to be more active and stable in organic solvents. The optimum water activity (a _w ) for reaction was also shifted by using modified enzymes. Changes in enantioselective behavior were also observed.     

层状硅酸盐固定化肌红蛋白在有机溶剂中的催化活性和稳定性

在温和条件(室温及pH=7)下,通过剥离重组实现了肌红蛋白分子在层状硅酸盐magadiite纳米粒子层间的固定化,系统考察了固定化后肌红蛋白在不同疏水度的有机溶剂中催化邻苯二胺氧化反应的性能.结果表明,固定化肌红蛋白在中等疏水度的有机溶剂中呈现出比自由肌红蛋白更高的催化活性和稳定性.结合固定化肌红蛋白在有机溶剂中的动力学研究结果,初步探讨了其具有高催化活性的原因.     

Enhanced catalytic activity of hemoglobin in organic solvents by layered titanate immobilization

A simple layered titanate immobilization can significantly enhance the Hb catalytic activity in organic media relative to native Hb, especially in hydrophilic dioxane systems, where the composites have an about 100 times enhancement. The interlayer water should be responsible for the increased nonaqueous catalytic activities of the immobilized Hb due to its strengthened resistance to the distorting of the Hb surface essential water layer by organic solvents.     

Esterification and transesterification with immobilized lipase in organic solvent

In this paper, we report the reactions of esterification and transesterification catalyzed by the following lipase adducts in organic solvents: (1) glass-adsorbed; (2) acetone precipitated on porous glass, kieselghur-adsorbed; (3) Al₂O₃-adsorbed; and (4) agar bead-adsorbed. The optimal water content varied for different forms of the enzymes. Under the most favorable conditions, kieselguhr-adsorbed and agar bead-adsorbed lipases, which have higher catalytic activities in organic solvents, are the best of all forms of lipases.     

Optimising biocatalyst design for obtaining high transesterification activity by α-chymotrypsin in non-aqueous media

Background  

Enzymes are often used in organic solvents for catalyzing organic synthesis. Two enzyme preparations, EPRP (enzyme precipitated and rinsed with n-propanol) and PCMC (protein coated microcrystals) show much higher activities than lyophilized powders in such systems. Both preparations involve precipitation by an organic solvent. The clear understanding of why these preparations show higher catalytic activity than lyophilized powders in organic solvents is not available.     

Xanthone Receptors as Oxyanion‐Hole Mimics in Artificial Enzymes

Different xanthone‐based receptors ( 2 – 10 ) for lactones and lactams have been prepared, and the feasibility of these compounds to mimic the known enzymatic ‘oxyanion‐hole’ structure is discussed. The self‐association of the receptors was found to pose a serious drawback for complex formation. X‐Ray crystal structures of receptor dimers allowed us to understand the reasons for their self‐association and to improve the design of the catalysts. The catalytic activity of the receptors has been tested towards the nucleophilic addition of pyrrolidine to unsaturated lactones. Since the resulting complexes were very weak in organic solvents, new receptors were developed for lactams, which showed better stabilities, and their catalytic activities were studied.     

水溶性金属卟啉应用于催化反应的研究进展

综述了水溶性金属卟啉作为催化剂应用于均相或非均相的催化反应的研究进展,重点介绍了水溶性金属卟啉在水或水与有机溶剂混合介质中催化底物氧化反应的催化性能,其中包括烷烃的羟基化,烯烃的环氧化,含氧、含硫及含氮化合物的氧化反应.另外水溶性金属卟啉还可用于催化Suzuki-Miyaura反应、氧化偶联反应、C=C氧化断裂反应等.水溶性金属卟啉催化剂具有水溶性、催化效率高、反应条件温和等优点,因此将在催化反应特别是氧化反应中得到更广泛的应用.     

官能化硅胶负载Pd—Cu催化剂的制备及催化芳香氯化物水相脱氯作用

将聚乙烯吡烷酮（PVP）与双金属Pd^2 、Cu^2 配位后,再负载于用平均分子量为600的聚乙二醇（PEG）官能化的硅胶上（SiO2-PEG600),制成一种新型双负载双金属催化剂PVP-PdCl2-CuCl2/SiO2-PEG600,将其用于催化难溶于水的芳香卤化物水相脱卤,在无需加入任何有机溶剂的情况下,对芳香氯化物呈现出高的脱氯活性和选择性,并具有良好的重复使用性能。通过IR、TEM、比表面积测定等手段,探讨了催化剂各组分在催化脱卤中的作用及可能的催化脱卤机理。     

Novel non-aqueous Fe(III)/Fe(II) redox couple for the catalytic oxidation of hydrogen sulfide to sulfur by air

A series of Fe(III) salts and organic solvents have been screened to develop novel non-aqueous catalysts for the conversion of H2S to sulfur. FeCl3/95% N-methylpyrrolidinone/5% H2O was found to be a most efficient non-aqueous system. The process chemistry, the proposed mechanism of catalytic oxidation of H2S, and the electrochemistry are discussed.     

Synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles

In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized by a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently chemically reduced to yield nearly size-monodisperse particles having dimensions of less than 3 nm. Monometallic, bimetallic (including core/shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica but also to stabilize the nanoparticle, makes it possible to tune solubility, and provides a means for immobilization of the nanoparticle on solid supports. These materials have a number of potential applications, but the focus here is on catalysis. Homogeneous catalytic reactions, including hydrogenations, Heck coupling, and Suzuki reactions, in water, organic solvents, biphasic fluorous/organic solvents, and liquid and supercritical CO2 are discussed. In many cases it is easy to recycle catalytic DENs. DENs can also be immobilized on supports, such as silica and titania, and used for heterogeneous catalysis. Bimetallic DENs are shown to have particularly interesting catalytic properties. In addition to a discussion of current progress in this field, a number of intriguing questions related to the properties and potential applications of these materials are examined.